Index: src/OFCharacterSet.m
==================================================================
--- src/OFCharacterSet.m
+++ src/OFCharacterSet.m
@@ -19,23 +19,30 @@
 
 #import "OFCharacterSet.h"
 #import "OFBitSetCharacterSet.h"
 #import "OFInvertedCharacterSet.h"
 #import "OFRangeCharacterSet.h"
+
+#import "once.h"
+
+@interface OFPlaceholderCharacterSet: OFCharacterSet
+@end
+
+@interface OFWhitespaceCharacterSet: OFCharacterSet
+@end
 
 static struct {
 	Class isa;
 } placeholder;
 
 static OFCharacterSet *whitespaceCharacterSet = nil;
 
-@interface OFPlaceholderCharacterSet: OFCharacterSet
-@end
-
-@interface OFWhitespaceCharacterSet: OFCharacterSet
-- (instancetype)of_init;
-@end
+static void
+initWhitespaceCharacterSet(void)
+{
+	whitespaceCharacterSet = [[OFWhitespaceCharacterSet alloc] init];
+}
 
 @implementation OFPlaceholderCharacterSet
 - (instancetype)init
 {
 	return (id)[[OFBitSetCharacterSet alloc] init];
@@ -100,11 +107,14 @@
 	return [[[self alloc] initWithRange: range] autorelease];
 }
 
 + (OFCharacterSet *)whitespaceCharacterSet
 {
-	return [OFWhitespaceCharacterSet whitespaceCharacterSet];
+	static of_once_t onceControl = OF_ONCE_INIT;
+	of_once(&onceControl, initWhitespaceCharacterSet);
+
+	return whitespaceCharacterSet;
 }
 
 - (instancetype)init
 {
 	if ([self isMemberOfClass: [OFCharacterSet class]]) {
@@ -137,38 +147,15 @@
 }
 
 - (OFCharacterSet *)invertedSet
 {
 	return [[[OFInvertedCharacterSet alloc]
-	    of_initWithCharacterSet: self] autorelease];
+	    initWithCharacterSet: self] autorelease];
 }
 @end
 
 @implementation OFWhitespaceCharacterSet
-+ (void)initialize
-{
-	if (self != [OFWhitespaceCharacterSet class])
-		return;
-
-	whitespaceCharacterSet = [[OFWhitespaceCharacterSet alloc] of_init];
-}
-
-+ (OFCharacterSet *)whitespaceCharacterSet
-{
-	return whitespaceCharacterSet;
-}
-
-- (instancetype)init
-{
-	OF_INVALID_INIT_METHOD
-}
-
-- (instancetype)of_init
-{
-	return [super init];
-}
-
 - (instancetype)autorelease
 {
 	return self;
 }
 

Index: src/OFInvertedCharacterSet.h
==================================================================
--- src/OFInvertedCharacterSet.h
+++ src/OFInvertedCharacterSet.h
@@ -23,10 +23,9 @@
 {
 	OFCharacterSet *_characterSet;
 	bool (*_characterIsMember)(id, SEL, of_unichar_t);
 }
 
-- (instancetype)of_initWithCharacterSet: (OFCharacterSet *)characterSet
-    OF_METHOD_FAMILY(init);
+- (instancetype)initWithCharacterSet: (OFCharacterSet *)characterSet;
 @end
 
 OF_ASSUME_NONNULL_END

Index: src/OFInvertedCharacterSet.m
==================================================================
--- src/OFInvertedCharacterSet.m
+++ src/OFInvertedCharacterSet.m
@@ -26,17 +26,23 @@
 - (instancetype)init
 {
 	OF_INVALID_INIT_METHOD
 }
 
-- (instancetype)of_initWithCharacterSet: (OFCharacterSet *)characterSet
+- (instancetype)initWithCharacterSet: (OFCharacterSet *)characterSet
 {
 	self = [super init];
 
-	_characterSet = [characterSet retain];
-	_characterIsMember = (bool (*)(id, SEL, of_unichar_t))
-	    [_characterSet methodForSelector: @selector(characterIsMember:)];
+	@try {
+		_characterSet = [characterSet retain];
+		_characterIsMember = (bool (*)(id, SEL, of_unichar_t))
+		    [_characterSet methodForSelector:
+		    @selector(characterIsMember:)];
+	} @catch (id e) {
+		[self release];
+		@throw e;
+	}
 
 	return self;
 }
 
 - (void)dealloc

Index: src/OFURL.m
==================================================================
--- src/OFURL.m
+++ src/OFURL.m
@@ -32,44 +32,70 @@
 #endif
 
 #import "OFInvalidArgumentException.h"
 #import "OFInvalidFormatException.h"
 #import "OFOutOfMemoryException.h"
+
+#import "once.h"
+
+@interface OFURLAllowedCharacterSetBase: OFCharacterSet
+@end
+
+@interface OFURLAllowedCharacterSet: OFURLAllowedCharacterSetBase
+@end
+
+@interface OFURLSchemeAllowedCharacterSet: OFURLAllowedCharacterSetBase
+@end
+
+@interface OFURLPathAllowedCharacterSet: OFURLAllowedCharacterSetBase
+@end
+
+@interface OFURLQueryOrFragmentAllowedCharacterSet: OFURLAllowedCharacterSetBase
+@end
 
 static OFCharacterSet *URLAllowedCharacterSet = nil;
 static OFCharacterSet *URLSchemeAllowedCharacterSet = nil;
 static OFCharacterSet *URLPathAllowedCharacterSet = nil;
 static OFCharacterSet *URLQueryOrFragmentAllowedCharacterSet = nil;
 
-@interface OFURLAllowedCharacterSetBase: OFCharacterSet
-- (instancetype)of_init OF_METHOD_FAMILY(init);
-@end
-
-@interface OFURLAllowedCharacterSet: OFURLAllowedCharacterSetBase
-+ (OFCharacterSet *)URLAllowedCharacterSet;
-@end
-
-@interface OFURLSchemeAllowedCharacterSet: OFURLAllowedCharacterSetBase
-+ (OFCharacterSet *)URLSchemeAllowedCharacterSet;
-@end
-
-@interface OFURLPathAllowedCharacterSet: OFURLAllowedCharacterSetBase
-+ (OFCharacterSet *)URLPathAllowedCharacterSet;
-@end
-
-@interface OFURLQueryOrFragmentAllowedCharacterSet: OFURLAllowedCharacterSetBase
-+ (OFCharacterSet *)URLQueryOrFragmentAllowedCharacterSet;
-@end
+static of_once_t URLAllowedCharacterSetOnce = OF_ONCE_INIT;
+static of_once_t URLQueryOrFragmentAllowedCharacterSetOnce = OF_ONCE_INIT;
+
+static void
+initURLAllowedCharacterSet(void)
+{
+	URLAllowedCharacterSet = [[OFURLAllowedCharacterSet alloc] init];
+}
+
+static void
+initURLSchemeAllowedCharacterSet(void)
+{
+	URLSchemeAllowedCharacterSet =
+	    [[OFURLSchemeAllowedCharacterSet alloc] init];
+}
+
+static void
+initURLPathAllowedCharacterSet(void)
+{
+	URLPathAllowedCharacterSet =
+	    [[OFURLPathAllowedCharacterSet alloc] init];
+}
+
+static void
+initURLQueryOrFragmentAllowedCharacterSet(void)
+{
+	URLQueryOrFragmentAllowedCharacterSet =
+	    [[OFURLQueryOrFragmentAllowedCharacterSet alloc] init];
+}
 
 @interface OFInvertedCharacterSetWithoutPercent: OFCharacterSet
 {
 	OFCharacterSet *_characterSet;
 	bool (*_characterIsMember)(id, SEL, of_unichar_t);
 }
 
-- (instancetype)of_initWithCharacterSet: (OFCharacterSet *)characterSet
-    OF_METHOD_FAMILY(init);
+- (instancetype)initWithCharacterSet: (OFCharacterSet *)characterSet;
 @end
 
 bool
 of_url_is_ipv6_host(OFString *host)
 {
@@ -90,20 +116,10 @@
 
 	return hasColon;
 }
 
 @implementation OFURLAllowedCharacterSetBase
-- (instancetype)init
-{
-	OF_INVALID_INIT_METHOD
-}
-
-- (instancetype)of_init
-{
-	return [super init];
-}
-
 - (instancetype)autorelease
 {
 	return self;
 }
 
@@ -121,23 +137,10 @@
 	return OF_RETAIN_COUNT_MAX;
 }
 @end
 
 @implementation OFURLAllowedCharacterSet
-+ (void)initialize
-{
-	if (self != [OFURLAllowedCharacterSet class])
-		return;
-
-	URLAllowedCharacterSet = [[OFURLAllowedCharacterSet alloc] of_init];
-}
-
-+ (OFCharacterSet *)URLAllowedCharacterSet
-{
-	return URLAllowedCharacterSet;
-}
-
 - (bool)characterIsMember: (of_unichar_t)character
 {
 	if (character < CHAR_MAX && of_ascii_isalnum(character))
 		return true;
 
@@ -163,24 +166,10 @@
 	}
 }
 @end
 
 @implementation OFURLSchemeAllowedCharacterSet
-+ (void)initialize
-{
-	if (self != [OFURLSchemeAllowedCharacterSet class])
-		return;
-
-	URLSchemeAllowedCharacterSet =
-	    [[OFURLSchemeAllowedCharacterSet alloc] of_init];
-}
-
-+ (OFCharacterSet *)URLSchemeAllowedCharacterSet
-{
-	return URLSchemeAllowedCharacterSet;
-}
-
 - (bool)characterIsMember: (of_unichar_t)character
 {
 	if (character < CHAR_MAX && of_ascii_isalnum(character))
 		return true;
 
@@ -194,24 +183,10 @@
 	}
 }
 @end
 
 @implementation OFURLPathAllowedCharacterSet
-+ (void)initialize
-{
-	if (self != [OFURLPathAllowedCharacterSet class])
-		return;
-
-	URLPathAllowedCharacterSet =
-	    [[OFURLPathAllowedCharacterSet alloc] of_init];
-}
-
-+ (OFCharacterSet *)URLPathAllowedCharacterSet
-{
-	return URLPathAllowedCharacterSet;
-}
-
 - (bool)characterIsMember: (of_unichar_t)character
 {
 	if (character < CHAR_MAX && of_ascii_isalnum(character))
 		return true;
 
@@ -240,24 +215,10 @@
 	}
 }
 @end
 
 @implementation OFURLQueryOrFragmentAllowedCharacterSet
-+ (void)initialize
-{
-	if (self != [OFURLQueryOrFragmentAllowedCharacterSet class])
-		return;
-
-	URLQueryOrFragmentAllowedCharacterSet =
-	    [[OFURLQueryOrFragmentAllowedCharacterSet alloc] of_init];
-}
-
-+ (OFCharacterSet *)URLQueryOrFragmentAllowedCharacterSet
-{
-	return URLQueryOrFragmentAllowedCharacterSet;
-}
-
 - (bool)characterIsMember: (of_unichar_t)character
 {
 	if (character < CHAR_MAX && of_ascii_isalnum(character))
 		return true;
 
@@ -287,22 +248,23 @@
 	}
 }
 @end
 
 @implementation OFInvertedCharacterSetWithoutPercent
-- (instancetype)init
-{
-	OF_INVALID_INIT_METHOD
-}
-
-- (instancetype)of_initWithCharacterSet: (OFCharacterSet *)characterSet
+- (instancetype)initWithCharacterSet: (OFCharacterSet *)characterSet
 {
 	self = [super init];
 
-	_characterSet = [characterSet retain];
-	_characterIsMember = (bool (*)(id, SEL, of_unichar_t))
-	    [_characterSet methodForSelector: @selector(characterIsMember:)];
+	@try {
+		_characterSet = [characterSet retain];
+		_characterIsMember = (bool (*)(id, SEL, of_unichar_t))
+		    [_characterSet methodForSelector:
+		    @selector(characterIsMember:)];
+	} @catch (id e) {
+		[self release];
+		@throw e;
+	}
 
 	return self;
 }
 
 - (void)dealloc
@@ -323,11 +285,11 @@
 of_url_verify_escaped(OFString *string, OFCharacterSet *characterSet)
 {
 	void *pool = objc_autoreleasePoolPush();
 
 	characterSet = [[[OFInvertedCharacterSetWithoutPercent alloc]
-	    of_initWithCharacterSet: characterSet] autorelease];
+	    initWithCharacterSet: characterSet] autorelease];
 
 	if ([string indexOfCharacterFromSet: characterSet] != OF_NOT_FOUND)
 		@throw [OFInvalidFormatException exception];
 
 	objc_autoreleasePoolPop(pool);
@@ -334,43 +296,59 @@
 }
 
 @implementation OFCharacterSet (URLCharacterSets)
 + (OFCharacterSet *)URLSchemeAllowedCharacterSet
 {
-	return [OFURLSchemeAllowedCharacterSet URLSchemeAllowedCharacterSet];
+	static of_once_t onceControl = OF_ONCE_INIT;
+	of_once(&onceControl, initURLSchemeAllowedCharacterSet);
+
+	return URLSchemeAllowedCharacterSet;
 }
 
 + (OFCharacterSet *)URLHostAllowedCharacterSet
 {
-	return [OFURLAllowedCharacterSet URLAllowedCharacterSet];
+	of_once(&URLAllowedCharacterSetOnce, initURLAllowedCharacterSet);
+
+	return URLAllowedCharacterSet;
 }
 
 + (OFCharacterSet *)URLUserAllowedCharacterSet
 {
-	return [OFURLAllowedCharacterSet URLAllowedCharacterSet];
+	of_once(&URLAllowedCharacterSetOnce, initURLAllowedCharacterSet);
+
+	return URLAllowedCharacterSet;
 }
 
 + (OFCharacterSet *)URLPasswordAllowedCharacterSet
 {
-	return [OFURLAllowedCharacterSet URLAllowedCharacterSet];
+	of_once(&URLAllowedCharacterSetOnce, initURLAllowedCharacterSet);
+
+	return URLAllowedCharacterSet;
 }
 
 + (OFCharacterSet *)URLPathAllowedCharacterSet
 {
-	return [OFURLPathAllowedCharacterSet URLPathAllowedCharacterSet];
+	static of_once_t onceControl = OF_ONCE_INIT;
+	of_once(&onceControl, initURLPathAllowedCharacterSet);
+
+	return URLPathAllowedCharacterSet;
 }
 
 + (OFCharacterSet *)URLQueryAllowedCharacterSet
 {
-	return [OFURLQueryOrFragmentAllowedCharacterSet
-	    URLQueryOrFragmentAllowedCharacterSet];
+	of_once(&URLQueryOrFragmentAllowedCharacterSetOnce,
+	    initURLQueryOrFragmentAllowedCharacterSet);
+
+	return URLQueryOrFragmentAllowedCharacterSet;
 }
 
 + (OFCharacterSet *)URLFragmentAllowedCharacterSet
 {
-	return [OFURLQueryOrFragmentAllowedCharacterSet
-	    URLQueryOrFragmentAllowedCharacterSet];
+	of_once(&URLQueryOrFragmentAllowedCharacterSetOnce,
+	    initURLQueryOrFragmentAllowedCharacterSet);
+
+	return URLQueryOrFragmentAllowedCharacterSet;
 }
 @end
 
 @implementation OFURL
 + (instancetype)URL